Pneumatic radial tire with high durable bead portions

ABSTRACT

A pneumatic radial tire with high durable bead portions includes a pair of bead portions, a pair of sidewalls and a tread extending between the sidewalls, and further includes as a body reinforcement a carcass extending between the bead portions and consisting of plies whose cords are radially arranged. At least one ply being turned up about bead cores of the bead portions from inside to outside of the tire to form a turn-up portions. A carcass pass line in radial section of the tire in its self-holding position filled with 5% of a normal inner pressure under no-load condition includes curvature changing areas in a carcass profile curved toward the turned-up portions in the proximities of positions corresponding to a height of turn-up ends of the ply from a rim diameter line to cause compressive stresses in the bead portions near to the turn-up ends of the ply by deformations of the carcass when the normal inner pressure is filled in the tire. With the above arrangement, the durability at the bead portions of the tire is improved to an extent required for prolongation of life time obtained by recapping the tire repeatedly.

BACKGROUND OF THE INVENTION

This invention relates to a pneumatic radial tire having high by durablebead portions.

Heavy duty pneumatic radial tires to be used for trucks, buses and thelike are particularly required to have high durability of bead portions.Such a requirement results from not only the severe service conditionsbut also the fact that they are generally used repeatedly by recappingevery time tread rubbers have been torn off to realize their longestpossible effective life.

With such heavy duty pneumatic radial tires, failures at bead portionsare often found when they are inspected whether they are able to be usedagain by recapping. Such failures at the bead portions are mainly causedby high tensile strains in the proximities of turn-up ends of carcassplies, particularly radially outwards thereof. In most cases, thetensile strains give rise to rubber fatigue and separations.

In order to improve the durability of the bead portions, it has beenproposed to provide reinforcing members or other particular members tomitigate the above strains and to restrain any growth of cracks due tothe rubber fatigue. However, such an addition of the membersdetrimentally affects productivity of tires accompanying with increasedcost and the occurrence of heat.

In general, the heavy duty pneumatic radial tire to be used for trucksand buses comprises a pair of bead portions, sidewalls and a treadextending between the sidewalls and further comprises as a bodyreinforcement a carcass extending between the bead portions and havingplies whose cords are radially arranged. At least one ply of the carcassis folded from inside to outside about bead cores into a turn-upconstruction. In this case, the durability of the bead portions dependsupon the turn-up ends of the carcass. However, direct measures for theturn-up portions to solve these problems have been insufficient toobtain useful effects.

SUMMARY OF THE INVENTION

The inventors of this application have investigated and developed acarcass profile of heavy duty pneumatic radial tires capable ofimproving the durability of bead portions to meet the requirement ofrenewal of effective life over and over again by recapping withoutrequiring any particular reinforcing members or special members. Theinvention resides in the discovery that the turn-up ends of the carcassplies governing the durability of the bead portions are subjected toforces in pulling-out directions by filled inner pressure in the tire,while the sidewalls and bead portions are subjected to bending forces sothat high tensile strains occur in rubbers facing to the turn-up endsresulting in failures at the bead portions, and that compressivestresses introduced into the rubbers are effective in order to reducethe tensile strains (to obtain an effect reducing the tensile strainsand hence with residual tensile stresses actually).

It is an object of the invention to provide an improved heavy dutypneumatic radial tire which eliminates all the disadvantages of theprior art and improves the durability at bead portions to an extentrequired for prolongation of life time obtained by recapping the tirerepeatedly.

In order to accomplish this object of the invention, in a pneumaticradial tire with high durable bead portions, including a pair of beadportions, a pair of sidewalls and a tread extending between thesidewalls, and further including as a body reinforcement a carcassextending between the bead portions and consisting of plies whose cordsare radially arranged, at least one ply being turned up about bead coresof the bead portions from inside to outside of the tire in a turn-upconstruction, wherein a carcass pass line in radial section of the tirein its self-holding position filled with 5% of a normal inner pressureunder no-load condition comprises curvature changing areas (v) in acarcass profile curved toward the turned-up portions in the proximity ofpositions corresponding to a height (h) of turn-up ends of the ply froma rim diameter line (RL) to cause compressive stresses in the beadportions near the turn-up ends of the ply by deformations of the carcasswhen the normal inner pressure is filled in the tire.

In a preferred embodiment, each of said curvature changing areas (v) ofthe carcass pass line is smoothly continuous with a zone (w) adjacentthereto and having a curvature smaller than that of the curvaturechanging area (v) and has a center of curvature inside the tire, or thezone (w) is a zone (w') on a side remote from the bead core and smoothlycontinuous with the curvature changing area (v) through an inflectionpoint of the carcass pass line.

The curvature changing area (v) is positioned between points (M) and (N)spaced a distance (1) less than 10 mm apart from each other along thecarcass pass line and within a carcass pass line area extending radialdistances (g) corresponding to 8% of a maximum radial height (H) of thecarcass pass line from a rim diameter line (RL) on radially inward andoutward sides of the turn-up ends of the ply.

According to the invention a difference θ between angles of tangents(m--m') and (n--n') at the points (M) and (N) to the carcass line is 5°to 90°.

The zone (w) is a zone adjacent the curvature changing area (v) on aside remote from the bead core and radially extends to a point spacedfrom the height of the turn-up ends a distance (1) 24% of a maximumradial height (H) of the carcass pass line from a rim diameter line (HL)has a curvature within 1/500 (mm⁻¹) in a portion of the carcass passline between two points (S) and (T) spaced along the pass line adistance more than 12% of the maximum radial height (H).

The zone (w') on the side remote from the bead core includes two points(P) and (Q) spaced outwardly by radial distances (i) and (j)corresponding to 12 to 24% of a maximum radial height (H) of the carcasspass line from a rim diameter line (RL) and centers of curvatures of thepass line between the points (P) and (Q) are located out of the tire.

The tire preferably comprises wedge rubbers in the form of a convex lensin section along the curvature changing areas (v) inside of the carcass.

The tire according to the invention may comprise inner liners extendingalong an inner circumference of the carcass and each of the inner linerscomprises a thicker portion corresponding to the curvature changingportion (v) of the carcass pass line.

The thickness of the thicker portion of the inner liner is preferably1.7 to 8 times, more preferably 2 to 4 times an average thickness of theentire inner liner.

With the novel idea according to the invention, since tensile strainsoccurring in rubbers in the proximities of turn-up ends of carcass plyhaving cords radially arranged are eliminated with the aid of particularcarcass profile in the form of a toroidal shape of the carcass pass lineextending between bead portions without relying upon the turn-upportions themselves, any reinforcing members or particular membershitherto used as reinforcements are not needed in order to avoid anytroubles of the bead portions.

When measuring the carcass profiles, the measurement should be effectedafter keeping a tire filled with a normal inner pressure for about 24hours, or more preferably after running at a speed of 60 km/h under aload of the order of an empty car for about one hour, in order to removedeformations due to piled storing for a long time.

The invention will be more fully understood by referring to thefollowing detailed specification and claims taken in connection with theappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b, 2 and 3a-3c are sectional views exemplarilyillustrating carcass pass lines of tires according to the invention;

FIGS. 4-7 are sectional views illustrating sections of embodiments oftires according to the invention; and

FIG. 8 is a sectional view illustrating a section of another embodimentof a tire according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1a and 1b, 2 and 3a-3c illustrate one example of carcass profileof a radial tire according to the invention.

In each drawing, the tire comprises bead portions 1, sidewalls 2, atread 3, a carcass 4, an inner liner 5, bead cores 6, and a belt 7.Reference numeral 8 denotes a rim. Each figure shows a radial section ofone half of a left half of a tire or its principal portion. The carcass4 is schematically shown in thick solid lines. Bead reinforcing memberssuch as bead chafers and stiffeners are omitted in the drawings and theinner liners 5 are partially omitted as the case may be.

Plies of the carcass 4 having radially arranged cords are turned upabout the bead cores 6 from inside to outside of the tire. It is assumedthat a radial end of the turn-up end from the bead base or a rimdiameter line RL is h, while a maximum radial height of a pass line ofthe carcass 4 from the line RL is H. A curvature changing area v of thecarcass pass line is located between points M and N spaced a distance 1within 10 mm along the pass line in a first pass line area extendingover radial or vertical distance g on both sides of a line of the radialdistance h from the rim diameter line RL over radial or verticaldistances g which are 8% of the maximum height H. In this case, adifference between angles θ_(M) and θ_(N) is preferably 5°-90° where theangles θ_(M) and θ_(N) are formed by the rim diameter line RL andtangents m-m' and n-n' to the pass line of the carcass 4 at the points Mand N.

In a self-retaining or holding position of the --tire (refer to solidlines in FIG. 1b) when inner pressure is filled in the tire mounted onthe rim to 5% of a standard or normal inner pressure under no-loadcondition, the curvature changing area v of the carcass pass line curvestoward the turn-up end of the ply (concave as viewed from the inside ofthe tire) as shown in FIGS. 1a and 1b. Under the normal inner pressureas shown in broken lines in FIG. 1b, however, the pass line of thecarcass 4 is deformed so as to be smoothly continuous as the tire beinginflated owing to the inner pressure, with the result that compressivestresses are caused in the bead portions 1 in the proximities of theturn-up ends of the ply to mitigate the tensile strains.

As the compressive stresses serve to reduce the tensile strains underno-load and inner pressure filled condition, effective reduction intensile strain in the bead portions at the turn-up ends of the ply isaccomplished when the tire is running so that failures of the beadportions are effectively avoided.

FIG. 2 illustrates a zone w of a carcass pass line which is adjacent thecurvature changing area v on a side remote from the bead core 6 andradially outwardly extends to a point K spaced a distance j to i (FIG.1a) from the turn-up end of the carcass corresponding to 12-24% of themaximum radial height H of the pass line of the carcass 4. The carcasspass line within the zone W has a curvature within 1/500 (mm⁻¹).

Compressive stresses are caused in the bead portions to reduce thetensile strains in the same manner as that shown in FIG. 1a.

FIG. 3a illustrates a curvature changing area w' of a carcass pass linewhich is adjacent the area v on the side remote from the bead core 6 andradially outwardly extends to a point P spaced a distance j (FIG. 1a)from the turn-up end of the carcass corresponding to 12% of the maximumradial height H of the pass line of the carcass 4. The pass line of thecarcass 4 in the area w' between the points P and Q has a center of thecurvature out of the tire. As is clear from FIG. 3c, compressivestresses occur in the proximity of the turn-up ends to mitigate tensilestrains in the same manner as in FIG. 1a. The zone w is smoothlycontinuous with the curvature changing area v through an inflectionpoint of the carcass pass line.

According to the invention, by providing the curvature changing area vin the carcass pass line the durability of beads can be improved withtire constituting members as they are without changing the constructionof tires and members of bead portions. Therefore, the invention isadvantageous in quality and productivity of tires.

The particular carcass profile as above described can be obtained bycontrolling distribution of rubber thicknesses from inner walls to thecarcass ply on inner sides of axial directions of the tire in formingand vulcanizing the rubber. If it is needed to severely controlvariations and irregularities in the carcass line due to so-called"rubber flow", the following measures are effective.

With tires formed by conventional forming and vulcanizing methods, acarcass ply extending between bead cores is arranged along an innersurface of the tire. In contrast herewith, according to the invention,as shown in FIGS. 4, 5 and 7, wedge rubbers 9 in the form of a convexlens in section are previously arranged on an inner surface of thecarcass correspondingly to the carcass profile changing areas v or innerliners 5 are used which are formed with portions 5' having partiallydifferent thicknesses.

Moreover, the above curvature changing area v can be obtained in thecarcass pass line by providing a vulcanizing bladder with continuousridges at positions corresponding to the curvature changing area v.

Therefore, the variations and irregularities of the carcass pass line inproduction can be restrained with the aid of these measures in thismanner.

The tire according to the invention comprises carcass pass linecurvature changing area v in which the carcass profile in radial sectionis concave as viewed form the inside of the tire in the self-standingposition of the tire when 5% of a standard or normal inner pressure isfilled in the tire. When the tire is filled with the normal innerpressure, deformations in the carcass and the rubber accompanyingtherewith are caused concentrically in the concave portions and theproximities thereof so that the tensile strains occurring in the rubberat the bead portions facing to the turn-up portions of the carcass 4 aremitigated compensatingly by causing deformations concentrically in theconcave portions, thereby accomplishing the improvement of thedurability of the bead portions.

In order to concentrate the deformations in the concave portions, theconcave portions are required to have considerably large curvatures incomparison with the other portions and at the same time have portionsthat difference between angles of the tangents m--m' and n--n' to thecarcass pass line at the two points M and N spaced a distance less than10 mm along the carcass relative to the rim diameter line RL is morethan 5°.

In order to mitigate the tensile strains occurring at ends of the plywith the aid of the effect of the deformations concentrated in theconcave portions, moreover, the concave portions and the ends of the plymust be sufficiently adjacent each other. In other words, the concaveportions must be arranged on the carcass pass line within the rangebetween the heights h-g and h+g from the rim diameter line RL as shownin FIGS. 1-3 where the distance g is 8% of the maximum height H of thecarcass line.

Although it is required for the concave portions to have curvatureslarge enough in comparison with those of the other portions of thecarcass, if such large curvatures exist in a too wide range of thecarcass, the required concentration of deformations cannot beaccomplished when the normal inner pressure is filled in the tire.

It is therefore needed to provide portions having small curvatures onsides of the tire rotational axis and tire tread with respect to theconcave portions. However, since the stiffeners and chafers asreinforcing members are arranged on the side of the rotating axis of thetire, the rigidity of the carcass on this side is very high. Therefore,the carcass profile on this side is not susceptible to deformation ofthe tire caused by filling the inner air pressure. Accordingly, it isdesired to make the curvatures small enough over sufficient length morethan 12% of the maximum height H of the carcass line adjacent theconcave portions on the side of the tread with radii of curvature morethan 500 mm as shown in FIGS. 1a and 1b.

Instead of the portions of the carcass line having small radii ofcurvature, the carcass line may have portions which form convex portionsas viewed from inside the tire. With such a feature, the deformations ofthe tire can be concentrated into the concave portions when filling thenormal inner pressure to reduce the strains at the ends of the carcassply, thereby improving the durability of the bead portions.

In other words, as shown in FIGS. 3a-3c, it is effective that thecarcass ply 4 has a convex portion as viewed from the inside of the tirewithin a range between 24% of the maximum height H of the carcass linefrom the height h at the end of the carcass ply on the tread side of theline of the height h and 8% of the maximum height H on the side of thetire rotating axis. The range is preferably between 12% of the maximumheight H on the tread side and 8% of the maximum height H on the tirerotating axis.

In order to bring carcass pass lines of the tires into control ofvariations and irregularities in production of tires due to "rubberflow" in vulcanization according to the invention, it is effective toarrange wedge rubbers 9 in the proximity of the concave portions onaxially inner sides of the carcass ply to make smooth the inner walls ofthe tire or to form convex portions viewed from the inner side of thetire rotating axis.

It is recommendable for the same purpose to partially changing thethicknesses of the inner liners 5 in the proximities of the concaveportions as shown in FIG. 8, although it is uniform in thickness in theconventional form.

In order to sufficiently restrain variation in carcass pass line, it ismore desirable to have thicknesses of the inner liners in theproximities of the concave portions 1.7 to 8 times, preferably 2 to 4times an average thickness of the entire inner liners.

Example 1

FIG. 4 illustrates one embodiment of the invention which is a lugpattern tire (size: 10.00 R20) having two nylon chafers and one wirechafer as shown in the drawing. A maximum height H of the carcass linefrom a rim diameter line RL is 233 mm. A height h of ply ends is 66.5mm. Two points M and N on the carcass line are positioned at heights 72mm (h+0.024 H) and 65.5 mm (h-0.004 H) respectively and spaced 7 mm fromeach other. A difference between angles of tangents at the points M andN to the carcass pass line relative to the rim diameter line RL is 6.0°.

Adjacent the concave portions as viewed from inside of the tire,portions of the carcass pass line on the side of the tread aresubstantially straight line in section over 30 mm (0.129H) length. Onthe other hand, rubbers in the form of a lens in section having 20 mmwidth and 2 mm maximum thicknesses are arranged between the carcass plyand the nylon chafer adjacent thereto.

Tires as above described were produced by way of trial and durability atbead portions of these tires was tested in a drum running test. In thedrum test, a tire to be tested was urged against a drum and the drum wasrotated to drive the tire. A running distance of these tires increasedabout 16% in comparison with tires of natural equilibrium carcassprofile according to the prior art.

Example 2

FIG. 5 illustrates another embodiment of the tire according to theinvention which is a rib pattern tire (size: 10.00 R20) having two nylonchafers and one wire chafer. A maximum height H of the carcass line froma rim diameter line RL is 241 mm and a height h of ply ends is 67 mm.Two points M and N on the carcass pass line are positioned at heights65.7 mm (h-0.005H) and 59.2 mm (h-0.032H) respectively and spaced 7.8 mmfrom each other. A difference between angles of tangents at the points Mand N to the carcass line relative to the rim diameter line is 14°.

Adjacent the concave portions as viewed from an inside of the tire,portions of the carcass ply on the side of the tread and extending to aheight of 90 mm (h+0.099H) form convex portions as viewed from theinside of the tire. On the other hand, wedge rubbers in the form of aconvex lens in section having 20 mm width and 2.7 mm maximum thicknessesare arranged on an axial inside of an inner liner.

Tires as above described were produced by way of trial and durability atbead portions of these tires was tested in the drum running test. It wasfound in the test that a running distance of these tires increased about15% in comparison with tires of natural equilibrium carcass profileaccording to the prior art.

Example 3

FIG. 6 illustrates a further embodiment of the tire according to theinvention which is a rib pattern tire (size: 10.00 R20) having two nylonchafers and one wire chafer. A maximum height H of the carcass line froma rim diameter line RL is 241 mm and a height of the ply ends is 67 mm.Two points M and N on the carcass pass line are positioned at heights68.3 mm (h+0.005H) and 62.8 mm (h-0.017H) respectively and spaced 6 mmfrom each other. A difference between angles of tangents at the points Mand N to the carcass pass line relative to the rim diameter line RL is6.0°.

Adjacent the concave portions as viewed from an inside of the tire,portions of the carcass ply on the side of the tread and extending to aheight of 95 mm (h+0.116H) form convex portions as viewed from theinside of the tire.

Tires as above described were produced by way of trial and durability atbead portions of these tires was tested in the drum running test. It wasfound in the test that a running distance of these tires increased about18% in comparison with tires of natural equilibrium carcass profileaccording to the prior at.

Example 4

FIG. 7 illustrates a further embodiment of the tire according to theinvention which is a block pattern tire (size: 11/70 R22.5) having twonylon chafers and one wire chafer. A maximum height H of the carcassline from a rim diameter line RL is 165.5 mm and a height h of ply endsis 34 mm. Two points M and N on the carcass path line are positioned atheights 46.3 mm (h+0.074H) and 42.1 mm (0.049H) respectively and spaced5.2 mm from each other. A difference between angles of tangents at thepoints M and N to the carcass line relative to the rim diameter line is8.5°.

Adjacent the concave portions as viewed from an inside of the tire,portions of the carcass pass line on the side of the tread aresubstantially straight line in section over 22 mm (0.133H) length. Onthe other hand, reinforcing rubbers in the form of a lens in sectionhaving 20 mm width and 2.5 mm maximum thicknesses are arranged betweenthe two chafers.

Tires as above described were produced by way of trial and durability atbead portions of these tires was tested in the drum running test. Arunning distance of these tires increased about 12% in comparison withtires of natural equilibrium carcass profile according to the prior art.

As can be seen from the above description, according to the inventionthe durability at bead portions of heavy duty radial tires can beassuredly improved to an extent required for prolongation of life timeobtained by recapping the tire repeatedly.

It is further understood by those skilled in the art that the foregoingdescription is that of preferred embodiments of the disclosed tires andthat various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof.

What is claimed is:
 1. A pneumatic radial tire with durable beadportions, comprising a pair of bead portions, a pair of sidewalls and atread extending between the sidewalls, a carcass extending between thebead portions and consisting of plies whose cords are radially arranged,at least one ply being turned up about bead cores of the bead portionsfrom inside to outside of the tire in a turn-up construction, a carcasspass line in radial section of the tire in its self-holding positionfilled with 5% of a normal inner pressure under no-load conditioncomprises curvature changing areas (v) in a carcass profile curvedtoward the turned-up portions in the proximities of positionscorresponding to a height (h) of turn-up ends of the ply from a beadbase line to cause compressive stresses in the bead portions near theturn-up ends of the ply by deformations of the carcass when the tire isinflated to normal inner pressure; wherein each of said curvaturechanging areas (v) of the carcass pass line is smoothly continuous witha zone (w) adjacent thereto and said zone (w) having a curvature smallerthan that of the curvature changing area (v), said curvature changingarea has a center of curvature inside the tire, and is positionedbetween two points (M, N) spaced a distance less than 10 mm apart fromeach other along the carcass pass line and said curvature changing areais within a carcass pass line area extending a radial distancecorresponding to 8% of a maximum radial height (H) of the carcass passline from the bead base line on radially inward and outward sides of theturn-up ends of the ply, and wherein a difference θ between angles oftangents (m--m') and (n--n') at said two points (M, N) to the carcassline is in the range of 5° to 90°.
 2. A pneumatic radial tire as setforth in claim 1, wherein said zone (w) is a zone adjacent the curvaturechanging area (v) on a side remote from the bead core and has acurvature less than 1/500 (mm⁻¹) in a portion of the carcass pass linebetween two points (S) and (T) positioned within a carcass pass linearea radially extending to a point spaced from the height of the turn-upends a distance (i) 24% of a maximum radial height (H) of the carcasspass line from the bead base line and, said two points (S) and (T)spaced along the pass line a distance more than 12% of the maximumradial height (H).
 3. A pneumatic radial tire as set forth in claim 1,wherein said tire comprises wedge rubbers in the form of a convex lensin section along the curvature changing areas (v) inside the carcass. 4.A pneumatic radial tire as set forth in claim 1, wherein said tirecomprises inner liners extending along an inner circumference of thecarcass and each of the inner liners comprises a thick portioncorresponding to the curvature changing portion (v) of the carcass passline.
 5. A pneumatic radial tire as set forth in claim 4, wherein athickness of the thick portion of the inner liner is 1.7 to 8 times anaverage thickness of the entire inner liner.
 6. A pneumatic radial tireas set forth in claim 5, wherein said thickness of the thick portion ofthe inner liner is 2 to 4 times the average thickness of the entireinner liner.